Q&A

If the Check Engine light is on the computer in your car sees a fault with the emission control system. If the fault has been corrected (say the gas cap was loose and you tightened it the car goes through a particular drive cycle (it may take a week or two) and if it sees no fault it will turn the light of itself, otherwise you need a scan tool to turn off the light, it attaches to a 16 pin diagnostic socket under the dash.